1. Field of the Invention
The present invention is broadly concerned with stiffness decoupling assemblies to be used in the construction of earthquake-resistant structures such as multi-story buildings, bridges, and smaller structures such as single family houses having basements. The assemblies of the invention effectively decouple the lateral stiffness of the structure in question from the load-bearing strength of the supporting column system for the structure. In this way, the dynamic behavior of a structure under seismic excitation is effectively controlled, while nevertheless retaining the necessary load-bearing strength, damping strength and natural period for the structure. Advantageously, the stiffness decouplers of the invention include a plurality of elongated, concrete-filled pipes rigidly secured to a structure, together with a surrounding, primary load-bearing column extending between an underlying foundation and the structure, and receiving the pipes; low-friction bearings are provided between the columns and structure, in order to permit relative lateral movement therebetween. In the case of single family houses or similar small structures, the basement walls can be used as the primary load-bearing member for the associated concrete-filled pipes.
2. Description of the Prior Art
Architects and structural engineers have long grappled with the problem of designing buildings, bridges or other structures in areas prone to seismic events. The recent earthquake in San Francisco is but one of many examples of the potentially catastrophic consequences of improper building design in such locales.
Many proposals have been made in the past aimed at increasing the safety of earthquake-resistance of various structures. In general, most modern day proposals have attempted to combine the qualities of strength (that is, the ability to withstand large forces while remaining elastic), deformability and energy-absorbing capacity. For example, it is known to employ large elastomeric bearings to support ductile reinforced concrete frame structures, in order to isolate the structure from its underlying foundation. However, such bearings can be expensive, land moreover some are subject to environmental degradation.
It has also been suggested in the past to make use of mild steel energy-absorbing devices which are rigid under service-type loading, but yield and absorb energy under large earthquake-type loading. Such schemes rely on the hysteretic energy-absorbing capacity of steel bars used as base-isolating devices.
Despite intensive on-going research in this area, however, workers in the art have failed to heretofore develop a truly effective base isolation system which is economical, easy to install, long-lived and capable of absorbing potentially destructive seismic forces while preventing collapse of the supported structure.